Brooklyn Democrat Simcha Felder declared yesterday that he’ll caucus with Republicans when he takes his Senate seat in January.

That could allow Republicans to keep their lone power base in state government.

Democrats were leading in races for 33 of 63 Senate seats, although at least one was too close to call, before losing Felder.

And four Democrats who broke away to create an independent conference last year could also form a coalition with Republicans — while GOP insiders speculated there could be more Democratic defections.

Felder was believed to be planning to side with Majority Leader Dean Skelos (R-Nassau) — who drew a new, heavily Orthodox Jewish district in this year’s redistricting to favor Felder.

What’s more, Skelos didn’t put any money into the campaign of the Russian-born Republican incumbent Felder defeated, David Storobin — who barely won a special election earlier this year in a soon-to-be-defunct district.

The Post reported earlier this week that the Rev. Al Sharpton’s public efforts to pressure Democrats to unite could push Felder to the GOP — and that former Majority Leader Malcolm Smith (D-Queens) was “open” to caucusing with Republicans.

Felder met with Skelos yesterday.

Afterward, he said in a statement, “I have been clear that I will work with any group of senators who have real economic-development and jobs-encouragement ideas, who plan to bring substantial tax relief to the people who elected me, who have compassion for the poor and respect for the middle class, who support the improvement of public education and a plan to ease the burden of tuition-paying parents across New York” — code for Yeshiva parents, among others.

Skelos would say only that issues important to constituents in Felder’s politically conservative district, “including economic development and job creation, reducing taxes and providing financial relief for hardworking families . . . have been our priorities in the past and will continue to be.”

Senate Democratic spokesman Mike Murphy said his conference remains “confident” of a Democratic majority next year.